From 5b8417bd7db8639c3e71464021bab2c1e7b7b700 Mon Sep 17 00:00:00 2001
From: "zhengxie.lj" <zhengxie.lj@alibaba-inc.com>
Date: Thu, 26 May 2016 23:52:18 +0800
Subject: [PATCH] check the start node for performance

---
 lib/scope.js | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/scope.js b/lib/scope.js
index c7269347..5d0fb308 100644
--- a/lib/scope.js
+++ b/lib/scope.js
@@ -89,8 +89,12 @@ SymbolDef.prototype = {
 
             // https://github.com/mishoo/UglifyJS2/issues/1095
             // prevent mangle name conflict while using `let` or `const`
-            if (this.orig[0] instanceof AST_SymbolBlockDeclaration)
-                s = s.parent_scope;
+            if (this.orig[0] instanceof AST_SymbolBlockDeclaration) {
+                var start = s.start;
+                if (start && start.type === 'keyword' && (start.value ==='default' || start.value === 'case')) {
+                    s = s.parent_scope;
+                }
+            }
 
             this.mangled_name = s.next_mangled(options, this);
             if (this.global && cache) {